The present invention relates to an image forming apparatus including a digital image processing device and, more particularly, to a digital copying machine, a laser printer, a digital facsimile, a copying machine having an analog device and digital device in combination, etc.
Conventionally, some digital copying machines are capable of overlay-copying. For example, in a well-known overlay function, a part of a first original is read so as to have a memory, such as a RAM, store it, and the stored data is read from the memory as image data in copying a second original, so that the second original can be copied with the image data overlaid.
In some apparatus, specific image data, for example, specific word data such as "SECRET" is stored in a memory in advance, so that an original can be copied with the image data overlaid through an overlay function.
In using an overlay function in a conventional digital copying machine and the like, it is not possible for image data of a first original, which is read from a memory, to be magnified so that the image data is overlaid on a second original and it is also not possible for the image data of the first original to be space-magnified so that it is overlaid on the second original. Herein, "space-magnifying" means resolving image data not successively into units of predetermined, dots and magnifying the image data by spacing the dot units outward with respect to one another.